A fast reservation mechanism which has the ability to allocate bandwidth within a short period of time is desirable in fast packet-switched networks with high-speed bursty connections. In these networks, the high-speed bursty connections alternate between periods requiring a bandwidth allocation at peak and no bandwidth. In networks employing a static bandwidth allocation technique, as the alternating periods increase, the static bandwidth allocation technique becomes less efficient because the high-speed bursty connections generally require a bandwidth allocation close to their peak rate irrespective of how often they actually need it.
To resolve the bandwidth allocation problems associated with high-speed bursty connections, bandwidth reservation protocols have been presented. One bandwidth reservation protocol is described in U.S. Pat. No. 5,081,620 by Girard et al which is hereby incorporated by reference. This bandwidth reservation protocol sends a call packet containing a desired bit rate (DEB) from a source node to the destination node where the source node desires to send data at the desired bit rate to the destination node.
In the preferred embodiment described by Girard, each switching node between the source and destination node receives the call packet and adds the value of the DEB to an appropriate reserved bit rate register in the switching node. The reserved bit rate register indicates the total bit rate reserved in the switching node for data flowing in the same direction in the switching node as the call packet.
If the value of the register is greater than a maximum disposable bit rate (DBmax) of the switching node, a bit in the call packet, the R/E bit, is changed to zero, otherwise the value of the R/E bit packet is not changed. Then, regardless of whether the DBmax value was exceeded in the switching node, the call packet is sent to the next switching node where the DEB is again added to the appropriate reserved bit rate register and then compared to the DBmax of this switching node.
When the call packet reaches the destination node, the R/E bit is evaluated. If the R/E bit is not set to zero, indicating no switching node in the path from the source to the destination node exceeded its DBmax upon the addition of DEB to its current reserved bit rate, a call packet is sent back to the source node from the destination node indicating that the DEB has been reserved and the source node may transmit data to the destination node along the path at the DEB.
When each switching node between the source and destination node can support the DEB of the source node, this reservation protocol reserves the bit rate in a time period approximately equal to the round trip propagation of the call packet. The reservation protocol, however, fails to address the ramifications of its protocol when one or more switching nodes cannot support the DEB of the source node. In addition, this reservation protocol does not support source nodes that while preferably desiring some maximum bit rate or bandwidth can still function with a bandwidth lower than the desired maximum bandwidth down to some minimally acceptable bandwidth.